Relevant print ram actuators are described in U.S. application Ser. No. 162,993, filed June 25, 1980, and U.S. Patent No. 4,371,857. They are intended in particular for use in impact printers.
A plurality of print hammer actuators are also known which operate to different principles.
In accordance with U.S. Pat. No. 27,175, the print hammers are supported by leaf springs, whose energy is stored in their deflected state and used for print hammer actuation. The print hammer is electromagnetically fired by discontinuing the excitation of an electromagnet retaining the print hammer.
Line printers with a plurality of character positions comprise so-called print hammer banks. These print hammer banks serve to accommodate individual print hammer units, each of which is associated with a particular print position. The print hammer bank described in U.S. Pat. No. 27,175 has a number of special features: The preloaded print hammers are held by an electromagnet common to all print hammers. The carrier of the electromagnet is fixed to leaf springs, is shiftable in parallel and performs a reciprocal movement perpendicularly to the print line. This reciprocal movement serves to return the print hammers after actuation. The individual print hammers are also provided with flexibly mounted damping elements. These elements absorb the energy of the returning print hammers and latch the print hammers by means of resilient latches until the magnet yokes of the holding magnet have seized the print hammers in this very forward position. In addition, the damping elements are fixed to a pivotable support spanning the various print positions and whose pivot point is staggered in a downward direction relative to the resilient latches. By means of a cam type drive, the support can be provided for a short time to release the print hammers.
In a typical high-speed impact printer, such as IBM printer Model 3203, each print hammer unit consists of a clapper magnet, a separate print hammer and a push rod for transferring the kinetic energy of the clapper armature to the print hammer. By means of two screws, each electromagnet is screwed to a base plate common to all print units. Each time the flight time is adjusted, these screws have to be loosened and subsequently retightened. Each electromagnet fully transfers the recoil occurring during the acceleration of the armature to the base plate. It is not possible to exchange individual print hammers.
In addition, U.S. Pat. No. 4,388,861 describes a bank for accommodating several print ram units, which meets the following requirements:
each print ram unit is individually exchangeable without diassembling the bank;
the full recoil pulse is not transferred to the bank; and
few fixing elements are required for assembling the various print ram units.
The print ram units of this bank consist of a flat, narrow frame. In a recess of the frame an electromagnetic actuator is positioned for a ram guided in two bores of the frame. For accommodating and guiding the individual ram units, the bank has an essentially U-shaped cross-section. At least on one of its two ends, the frame of each ram unit is provided with a flexible pin arranged between two frame arms. The frames are detachably mounted between the U-arms of the bank. Both U-arms have recesses for positively or frictionally accommodating the front or rear frame part and the pin, respectively.
This bank described in the U.S. Pat. No. 4,388,861 above is particularly suitable for cylindrical print rams according to U.S. Pat. No. 4,371,857.